Generally, in a multi-layered device for modulating color or transmissivity employing an electrochromic material, a physical/chemical change is produced within the electrochromic material layer in response to electron or ion transfer caused by an externally applied electrical potential. This change results in modulation of the color and transmissivity of the device with respect to electromagnetic radiation directed thereagainst. Such devices generally comprise consecutive layers of an electrochromic material, an electrolyte-containing fast ion conducting material, and a counterelectrode. The exchange of ions between the electrochromic material and fast ion conducting layers, when an electrical potential is applied across the device, comprises the mechanism by which the electrochromic material layer becomes either bleached (substantially transparent, either lightly colored or colorless) or deeply colored (substantially opaque). By reversing the polarity of the electrical potential applied across the device, it may be "switched" between the bleached and opaque states. Depending upon the magnitude and duration of the applied electrical potential, an intermediate, generally colored, translucent state may be induced, wherein the electrochromic material layer contains a concentration of fast ions sufficient to reduce the transmissivity of the device to a desired level. Thus, depending upon the manner in which the device is operated, i.e., the polarity, magnitude, and duration of the voltage applied, it may be adjusted to have an electromagnetic radiation transmissivity from about 0% to greater than about 90%, with an inversely corresponding reflectivity.
In a typical electrochromic device, the electrochromic material layer comprises an inorganic metal oxide, most commonly a transition metal oxide such as, for example, tungsten oxide. Alternatively, the electrochromic material layer may comprise an electroconductive polymer such as an unsubstituted or substituted polyaniline. The electrolyte-containing fast ion conducting layer adjacent the electrochromic material layer is generally adapted to provide a positively charged light cation such as, for example, a lithium ion for insertion into the electrochromic material layer. As an example of the operation of a typical electrochromic device, when lithium ions are introduced into a tungsten oxide electrochromic material layer, the layer changes from a colorless transparent state to a dark blue-black color. Where the tungsten oxide electrochromic material layer is sufficiently thick, the induced coloration causes the tungsten oxide electrochromic material layer to become highly absorbing opaque to electromagnetic radiation, e.g., radiation in the visible portion of the electromagnetic spectrum.
The counterelectrode of an electrochromic device generally comprises a transition metal oxide layer such as, for example, vanadium oxide or tungsten oxide, or an electroconductive polymer such as, for example, a polypyrrole or polythiophene.
The electrolyte-containing fast ion conducting layer may be a liquid electrolyte solution such as, for example, lithium perchlorate in propylene carbonate, a gel such as, for example, a solution of polyvinyl butyral in methanol doped with lithium chloride, or a solid such as, for example, a cured polyurethane containing a lithium compound.
Where the fast ion conducting layer is a liquid or gel, the spacing between the apposing surfaces of the electrochromic material layer and the counterelectrode generally is established and maintained by glass beads or plastic spacers imbedded in the fast ion conducting layer. This construction also requires a seal at the peripheral edge of the device, to prevent leakage of the liquid or gel fast ion conducting material.
It is important to establish a uniform thickness for the fast ion conducting layer. This will assist in providing uniform coloration of the electrochromic device. Thus, glass beads or plastic spacers have been used in the prior art to maintain a precise gap between the electrochromic material layer and the counterelectrode.
Where the fast ion conducting layer is a solid polymeric material, glass beads or plastic spacers are likewise used to establish and maintain the spacing between the apposing surfaces of the electrochromic material layer and the counterelectrode while the fast ion conducting polymeric material cures to form a solid. However, the curing fast ion conducting polymer often shrinks during the curing process, causing the polymeric fast ion conducting layer to pull away from one or both of the electrochromic material layer and the counterelectrode. Consequently, the communication of fast ions between the electrochromic material layer and the cured solid polymeric fast ion conducting layer is diminished, resulting in poor coloring uniformity. Moreover, the glass beads or plastic spacers result in inoperative areas of the device.
U.S. Pat. No. 4,435,048 to Kamimori et al. discloses an electro-optical light controlling device, comprising consecutively an electrochromic material layer, a non-liquid electrolyte layer, and an electrode, wherein glass beads are used to establish a constant spacing between the electrochromic material layer and the electrode. Japanese Patent Application Publication No. 59-185328 illustrates the use of glass spacers between the electrochromic layers of a transmittance-adjustable glass panel.
It would be desirable to devise a process for preparing a solid polymeric fast ion conducting layer for an electrochromic device, which does not require the use of glass beads or plastic spacers. Such a process would result in a device wherein the fast ion conducting layer intimately contacts both the electrochromic material layer and the counterelectrode, and wherein the solid polymeric fast ion conducting layer would be devoid of inoperative areas.